This invention relates to a single component toner for developing electrostatic latent images in electrophotography, electrostatic recording, electrostatic printing and the like.
Electrostatic latent images can be made visible by single-component developer composed only of toner by means of normal development or reverse development to form copied images of high quality. Such a technique is disclosed in, for example, U.S. Pat. No. 3,731,146 and U.S. Pat. No. 2,811,465.
In single-component developing system, a toner levelling member (a blade) is pressed against a toner transporting member (a sleeve), toner particles pass through the space between the levelling blade and the sleeve to be charged electrically and a thin layer of charged toner particles is formed on the sleeve. It is required that the thin layer is formed stably on the sleeve to develop well electrostatic latent images formed on a photosensitive member.
With respect to the blade, an elastic blade formed of silicon rubber and the like is proposed to be pressed against the sleeve (as disclosed in U.S. Pat. No. 3,372,675, U.S. Pat. No. 3,426,730, JP Laid-Open 52-143831, JP Laid-Open 54-51848 and the like). Preferable blade is formed of rigid body such as SUS and the like from the viewpoints of prevention from wearing by toner particles and of linearity at the pressed portion on the photosensitive member so that more uniform thin layer of toner particles may be formed.
In either case where the elastic blade or the rigid blade is used, the toner particles are pressed at the toner levelling portion where the thin toner layer is formed, so that heat and stress are provided for the toner particles in single-component developing system. When a conventional toner formed of general styrene-acrylic resin is merely applied to the single-component developing system, toner particles deform plastically by stress caused by heat and pressure, so that the toner particles adhere to the blade and the sleeve. This phenomenon is inevitable in the single-component developing system. Such adherence of toner particles to the levelling member causes irregularity of toner thin layer, toner-providing failure and surface pollution of the developing sleeve. The adhered layer also causes deterioration of charging ability to result in irregular density of copied images, fogs on the copy ground and toner scattering.
On the other hand, an agent for fluidization, such as silica and the like, is generally added to toner in order to improve fluidity of a developer. When such a developer as containing the agent for fluidization is applied to single-component developing system, good fluidity is achieved at the beginning in repetition process because silica particles are merely adhered electrostatically to the surface of toner particles. However, the silica particles are buried into toner particles while the copying process is repeated, so that the fluidity is lost gradually.
Further, a toner formed of urethane-modified polyester resin is disclosed in, for example, JP Laid-Open 63-56659. The toner disclosed therein is applied to a two-component developer and provided to be fixed at high-speed and at low-temperature in the two-component developing system. However, the urethane-modified polyester resin is prepared at the small isocyanate usage, so that the chain-prolongation reaction does not proceed so much. The obtained polyester resin is low in polymerization degree and has such a molecular weight that insoluble component can not be obtained. The toner is completely different from that of the present invention in application field, object, properties of polyester resin and the like.